Optical assembly including plenoptic microlens array

ABSTRACT

An optical assembly includes a solid spacing layer between a plenoptic microlens array (MLA) and a pixel-level MLA, avoiding the need for an air gap. Such an assembly, and systems and methods for manufacturing same, can yield improved reliability and efficiency of production, and can avoid many of the problems associated with prior art approaches. In at least one embodiment, the plenoptic MLA, the spacing layer, and the pixel-level MLA are created from optically transmissive polymer(s) deposited on the photosensor array and shaped using photolithographic techniques. Such an approach improves precision in placement and dimensions, and avoids other problems associated with conventional polymer-on-glass architectures. Further variations and techniques are described.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority as a continuation of U.S.Utility application Ser. No. 13/560,138 for “Optical Assembly IncludingPlenoptic Microlens Array,” filed Jul. 27, 2012, the disclosure of whichis incorporated herein by reference.

U.S. Utility application Ser. No. 13/560,138 claimed priority from U.S.Provisional Application Ser. No. 61/513,844 for “System and Method forManufacturing Plenoptic Microlens Array,” filed Aug. 1, 2011, thedisclosure of which is incorporated herein by reference.

The present application is further related to U.S. Utility applicationSer. No. 12/632,979 for “Light-field Data Acquisition Devices, andMethods of Using and Manufacturing Same,” filed Dec. 8, 2009, issued asU.S. Pat. No. 8,289,440 on Oct. 16, 2012, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an optical assembly including aplenoptic microlens array such as can be used in a light-field camera tocapture directional information for light rays passing through thecamera's optics.

BACKGROUND

Light-field cameras, which may also be referred to as plenoptic cameras,use a plenoptic microlens array (MLA), in combination with a photosensorarray, to capture directional information of light rays passing throughthe camera's optics. Such directional information can be used forproviding and implementing advanced display of and interaction withcaptured pictures, such as refocusing after capture. Such techniques aredescribed, for example, in Ng et al., “Light Field Photography with aHand-Held Plenoptic Camera”, Technical Report CSTR 2005-02, StanfordComputer Science, and in related U.S. Utility application Ser. No.12/632,979 for “Light-field Data Acquisition Devices, and Methods ofUsing and Manufacturing Same,” filed Dec. 8, 2009, the disclosure ofwhich is incorporated herein by reference.

Plenoptic microlens arrays are often manufactured using apolymer-on-glass approach, including a stamping or replication processwherein the plenoptic MLA is fabricated as a polymer attached to atransparent glass surface. Plenoptic MLAs can be constructed in such amanner using machines and processes available, for example, from SussMicroOptics of Neuchatel, Switzerland. The polymer-on-glass MLA array isplaced with the lens side down, such that incoming light passes throughthe glass and is then directed by the plenoptic MLA onto the surface ofa photosensor array.

Referring now to FIG. 1A, there is shown an example of an assembly 100for a light-field camera according to the prior art, wherein theplenoptic MLA 102, including any number of individual microlenses 116,is constructed using a polymer-on-glass approach, resulting in MLA 102being fabricated on glass 103. An air gap 105 has been introducedbetween plenoptic MLA 102 and photosensor array 101 of the device, toallow for light rays to be properly directed to correct locations onphotosensor array 101.

In general, existing techniques for manufacturing a light field sensorrequire that photosensor array 101 and plenoptic MLA 102 be fabricatedas separate components. These components may be assembled using amechanical separator that adds air gap 105 between the components. Suchan assembly process can be expensive and cumbersome; furthermore, theresulting air gap 105 is a potential source of misalignment,unreliability, and/or reduced optical performance. It is desirable toavoid such separate fabrication of parts and later assembly usingmechanical separation so as to improve manufacturing efficiency, and sothat precision in placement of the lens components can be achieved.

In many image capture devices, a different type of microlens array,referred to herein as a pixel-level microlens array, is used to improvelight capture performance and/or reduce crosstalk between neighboringpixels in a photosensor array 101. Referring now to FIG. 1B, there isshown an example of an assembly 150 according to the prior art. Relativeto FIG. 1A, this diagram is shown at much higher magnification.Microlenses 206 in pixel-level microlens array 202 direct incoming light104 so as to maximize the amount of light that reaches each individualphotosensor 106, and to avoid losing light that would otherwise hit theareas between individual photosensors 106. Such an arrangement is wellknown in the art, and may be included on many commercially availableimage sensors.

The plenoptic microlens array 102 depicted in FIG. 1A and thepixel-level microlens array 202 depicted in FIG. 1B serve completelydifferent purposes. In general, these two types of microlens arrays areconstructed to be of differing sizes and locations. For example, eachmicrolens 206 of pixel-level microlens array 202 may be approximately 2microns across, while each microlens 116 of the plenoptic microlensarray 102 may be approximately 20 microns across. These measurements aremerely examples. In general, pixel-level microlenses 206 may have a 1:1relationship with photosensors 106, while plenoptic microlenses 116 mayhave a 1:many relationship with photosensors 106.

Referring now to FIG. 2, there is shown an optical assembly 200including both a plenoptic MLA 102 and a pixel-level MLA 202 accordingto the prior art. Such an assembly 200 effectively combines thecomponents depicted and described in connection with FIGS. 1A and 1B.Here, plenoptic MLA 102 directs incoming light 104 toward pixel-levelMLA 202. Microlenses 206 in pixel-level MLA 202 then further directlight toward individual photosensors 106 in photosensor array 101. Inthe arrangement of FIG. 2, air gap 105 is provided between plenoptic MLA102 and pixel-level MLA 202.

As described above, plenoptic MLA 102 of FIG. 2 can be constructed usinga polymer-on-glass approach, wherein plenoptic MLA 102 is attached toglass surface 103. For example, plenoptic MLA 102 may be formed using amold that is stamped out using polymer and affixed to glass surface 103.The resulting plano-convex microlens assembly is positioned in a“face-down” manner as shown in FIG. 2, with the convex lens surfacesfacing away from the light source.

The inclusion of both a plenoptic MLA 102 and a pixel-level MLA 202serves to further complicate the construction of the image captureapparatus. Existing techniques offer no reliable method for constructingan image capture apparatus that employs both a plenoptic MLA 102 and apixel-level MLA 202, without introducing an air gap 105. Introduction ofsuch an air gap 105 potentially introduces further complexity, cost, andpotential for misalignment.

SUMMARY

According to various embodiments of the present invention, an improvedsystem and method of manufacturing an optical assembly including aplenoptic microlens array are described. Further described is animproved optical assembly including a plenoptic microlens array,fabricated according to such an improved manufacturing method. Thevarious systems, methods, and resulting optical assembly describedherein yield improved reliability and efficiency of production, andavoid many of the problems associated with prior art approaches.

According to various embodiments of the present invention, an opticalassembly including a plenoptic microlens array (MLA) is fabricatedwithout the need to introduce an air gap between the plenoptic MLA andother components of the optical system. In at least one embodiment, theplenoptic MLA, along with a solid spacing layer, is manufactured in sucha manner that it is integrated with the photosensor array. For example,in at least one embodiment, the plenoptic MLA is created from an opticalpolymer deposited on the photosensor array, and then shaped usingphotolithographic techniques. The use of the solid spacing layer avoidsthe need for an air gap between the plenoptic MLA and other components.

Such an approach improves precision in placement and dimensions, andavoids other problems associated with polymer-on-glass architectures.The use of a photolithographic process also allows the plenopticmicrolens array to be positioned in a face-up manner, so as to improveoptical performance. Misalignment and imprecision resulting fromassembly can also be reduced or eliminated. In addition, thephotolithographic approach allows for more precise alignment of theplenoptic microlens array relative to the photosensor array.

In at least one embodiment, the plenoptic MLA is constructed togetherwith a pixel-level MLA, without the need for an air gap between the twoMLA's. The plenoptic MLA, along with a solid spacing layer, arefabricated directly atop the pixel-level MLA. Such a technique providesthe added functionality associated with a pixel-level MLA while avoidingproblems associated with prior art approaches that involve the use of anair gap.

The present invention also provides additional advantages, as will bemade apparent in the description provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate several embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention according to the embodiments. One skilled inthe art will recognize that the particular embodiments illustrated inthe drawings are merely exemplary, and are not intended to limit thescope of the present invention.

FIG. 1A is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA constructed according to the priorart and positioned in a face-down manner.

FIG. 1B is a cross-sectional diagram depicting a detail of an opticalassembly including a pixel-level MLA constructed according to the priorart.

FIG. 2 is a cross-sectional diagram depicting a detail of an opticalassembly including both a plenoptic MLA positioned in a face-down mannerand a pixel-level MLA, according to the prior art.

FIG. 3 is a cross-sectional diagram depicting a detail of an opticalassembly including both a plenoptic MLA positioned in a face-up mannerand a pixel-level MLA, constructed according to an embodiment of thepresent invention.

FIG. 4 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, wherein theoptical assembly is fabricated without an air gap according to anembodiment of the present invention, and wherein the index of refractionof the plenoptic MLA and spacing layer is lower than that of thepixel-level MLA.

FIG. 5 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, wherein theoptical assembly is fabricated using a photolithographic processaccording to an embodiment of the present invention, and wherein theindex of refraction of the plenoptic MLA and spacing layer is higherthan that of the pixel-level MLA.

FIG. 6 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and two layers of pixel-level MLAs,wherein the optical assembly is fabricated using a photolithographicprocess according to an embodiment of the present invention.

FIG. 7 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, wherein thepixel-level MLA is fabricated using a material having a gradient indexof refraction (GRIN), according to an embodiment of the presentinvention.

FIG. 8 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, wherein thepixel-level MLA is fabricated in a manner that matches certain opticalproperties of the plenoptic MLA, according to an embodiment of thepresent invention.

FIG. 9 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, furtherincluding opaque microstructures to block stray light from neighboringmicrolenses in the plenoptic MLA, according to an embodiment of thepresent invention.

FIG. 10 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA having multiple layers, according toan embodiment of the present invention.

FIG. 11 is a cross-sectional diagram depicting a detail of an opticalassembly including a plenoptic MLA and a pixel-level MLA, illustratingmultiple steps involved in fabricating the optical assembly using aphotolithographic process according to an embodiment of the presentinvention.

FIG. 12 is a flow diagram depicting a method for fabricating an opticalassembly including a pixel-level MLA, spacing layer, and plenoptic MLA,according to an embodiment of the present invention.

FIG. 13 is a flow diagram depicting a method for fabricating an opticalassembly including a pixel-level MLA, spacing layer, plenoptic MLA, andopaque microstructures according to an embodiment of the presentinvention.

FIGS. 14A through 14C are a series of cross-sectional diagrams depictingan example of fabrication of a microlens array using a stamping method,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to various embodiments of the present invention, opticalassemblies are constructed that avoid the need for an air gap between aplenoptic microlens array (MLA) and other components. In at least oneembodiment, a photolithographic process is used, wherein a spacing layercontaining solid spacing material is introduced between the plenopticMLA and other components, so as to avoid the need for an air gap.

For illustrative purposes, various configurations of optical assembliesincluding plenoptic MLA's are described herein. One skilled in the artwill recognize that the particular configurations depicted herein areexemplary only, and that other configurations, arrangements, andmanufacturing techniques can be implemented without departing from theessential characteristics of the claimed invention.

In at least one embodiment, the various optical assemblies described anddepicted herein can be implemented as part of any suitable image capturedevice, such as a camera. For example, any of such optical assembliescan be implemented as part of a light-field camera such as described inNg et al., and/or in related U.S. Utility application Ser. No.12/632,979 for “Light-field Data Acquisition Devices, and Methods ofUsing and Manufacturing Same,” filed Dec. 8, 2009, the disclosure ofwhich is incorporated herein by reference. Such a light-field camera canbe designed to capture and store directional information for the lightrays passing through the camera's optics. Such directional informationcan be used for providing and implementing advanced display of andinteraction with captured pictures, such as refocusing after capture.One skilled in the art will recognize, however, that the techniquesdescribed herein can be applied to other types of devices andapparatuses, and are not necessarily limited to light-field cameras.

Referring now to FIG. 3, there is an optical assembly 300 including botha plenoptic MLA 102 and a pixel-level MLA 202, wherein plenoptic MLA 102is positioned “face-up”, i.e., with the convex lens surfaces facingtoward the light source, according to one embodiment of the presentinvention. In at least one embodiment, such a configuration can provideimproved optical performance. However, existing polymer-on-glassapproaches can make such an arrangement difficult to achieve, becauseglass 103 may be too thick to allow proper and accurate positioning ofthe convex lens elements of plenoptic MLA 102 at the appropriatedistance from pixel-level MLA 202.

The approaches in FIGS. 2 and 3 both involve separate construction ofphotosensor array 101 and plenoptic MLA 102; the components are thenassembled using a mechanical separator that adds air gap 105 between thecomponents. As discussed above, the resulting air gap 105 can also be asource of misalignment, unreliability, and/or reduced opticalperformance.

Integration of Plenoptic MLA with Photosensor Array

According to various embodiments of the present invention, an opticalassembly including plenoptic MLA 102 is fabricated without the need tointroduce an air gap between plenoptic MLA 102 and other components ofthe optical system. Referring now to FIG. 4, there is shown across-sectional diagram depicting a detail of optical assembly 400including both plenoptic MLA 102 and pixel-level MLA 202, constructedaccording to an embodiment of the present invention. Plenoptic MLA 102,along with layer 401 of spacing material, are manufactured in such amanner that they adjoin one another. Spacing layer 401 also adjoinspixel-level MLA 202. Such an arrangement avoids the need for an air gap.For example, in at least one embodiment, plenoptic MLA 102 and spacinglayer 401 are created from an optical polymer deposited or “spin-coated”on photosensor array 101, and then shaped using photolithographictechniques. Plenoptic MLA 102 and spacing layer 401 may be created atthe same time in a single process, or sequentially by first creatingspacing layer 401 and then adding plenoptic MLA 102. One method tocreate the profile for plenoptic MLA 102 is to use a gray-scale mask forphotolithography. Once cured, spacing layer 401 and plenoptic MLA 102are solid. One skilled in the art will recognize, however, that othertechniques can be used to generate an optical assembly 400 as shown inFIG. 4.

In the example of FIG. 4, the index of refraction of plenoptic MLA 102(and spacing layer 401) is lower than that of pixel-level MLA 202. Oneskilled in the art will recognize, however, that different materials,such as polymers of varying types or other materials of varyingrefractive indices can be used for the various layers and components. Asdescribed herein, variations in the indexes of refractions of thematerials can be exploited to achieve desired optical characteristics ofthe overall assembly 400.

For example, referring now to FIG. 5, there is shown a cross-sectionaldiagram depicting a detail of an optical assembly 500 wherein the indexof refraction of plenoptic MLA 102 (and spacing layer 401) is higherthan that of pixel-level MLA 202. Again, in at least one embodiment,such an assembly 500 can be fabricated using photolithographicprocesses.

In the examples of FIGS. 4 and 5, the shaping of the microlenses 206 inpixel-level MLA 202 is optimized to focus light on photosensors 106based on the optical interface between pixel-level MLA 202 and spacinglayer 401. In FIG. 4, the index of refraction R1 of plenoptic MLA 102and spacing layer 401 is lower than the index of refraction R2 ofpixel-level MLA 202. In this case, microlenses 206 in pixel-level MLA202 have a convex shape. Conversely, in FIG. 5, the index of refractionR2 of plenoptic MLA 102 and spacing layer 401 is higher than the indexof refraction R1 of pixel-level MLA 202. In this case, microlenses 206in pixel-level MLA 202 have a concave shape, so as to properly directlight rays onto photosensors 106.

As can be seen from the example configurations shown in FIGS. 4 and 5,the techniques of the present invention avoid the need for mechanicalspacing and an air gap, since spacing is accomplished via spacing layer401 deposited, for example, as part of the photolithographic process.This arrangement results in improved precision in placement of theplenoptic MLA 102.

In at least one embodiment, the techniques of the present inventionprovide improved horizontal and vertical alignment between plenoptic MLA102 and other components such as pixel-level MLA 202 and photosensorarray 101, by using the precise alignment techniques used inlithographic manufacture. Such improvements in horizontal (x-y)alignment help ensure that microlenses 116 of plenoptic MLA 102accurately direct light to appropriate locations along pixel-level MLA202. In at least one embodiment, plenoptic MLA 102 may be created in amanner such that each microlens 116 covers an integral number of pixels(for example, using a square layout with each plenoptic microlens 116covering an area corresponding to 10×10 photosensors 106 in photosensorarray 101). The improved vertical (z) alignment ensures that properfocus is obtained.

In addition, the techniques of the present invention provide reducederror. Lithographic depositing of materials to generate the microlensstructures has the potential to produce more precise optics thanconventional polymer-on-glass assemblies.

The techniques of the present invention can provide improved reliabilityand alignment of components, and can reduce manufacturing costs byremoving the need for mechanical separators to introduce an air gap.Furthermore, such techniques help to ensure that the plenoptic MLA 102is constructed in such a manner that the optical performance ofpixel-level MLA 202 is not unduly comprised.

Method of Manufacture

In at least one embodiment, the optical assemblies described herein aremanufactured using stamping to deposit and shape an optical materialdirectly onto photosensor array 101. The optical material can be anysuitable material, such as polymer that can be cured using ultravioletlight. The stamp forms the optical material into the desired shape,including, for example, the convex surfaces that will make up plenopticMLA 102. In at least one embodiment, the stamping can be performed usinga stamp that is transparent or semi-transparent to ultraviolet light,allowing the polymer to be cured while the stamp is in place. Such amechanism assures precise and accurate positioning of plenoptic MLA 102with respect to other components.

Referring now to FIG. 12, there is shown a flow diagram depicting amethod for fabricating an optical assembly including a pixel-level MLA202, spacing layer 401, and plenoptic MLA 102, according to anembodiment of the present invention. Referring also to FIG. 11, there isshown a cross-sectional diagram depicting a detail of an example of anoptical assembly 1100 constructed according to the method of FIG. 12.

One skilled in the art will recognize that the particular steps andsequence described and depicted herein are merely exemplary, and thatthe present invention can be practiced using other steps and sequences.One skilled in the art will recognize that the optical assembliesdescribed herein can be constructed using any suitable material orcombination of materials, and that the mention of particular materialsand/or properties of such materials herein is merely intended to beexemplary, and is not intended to limit the scope of the invention tothose particular materials/or properties of such materials. Inparticular, the example indexes of refraction depicted and describedherein are merely exemplary.

The method begins 1200. Pixel-level MLA 202 is created 1201, using, inat least one embodiment, a material with a very high index ofrefraction, such as silicon nitride, with an index of refraction ofapproximately 2.05. In at least one embodiment, lenses 206 ofpixel-level MLA 202 are made in a convex shape, and are positioneddirectly above photosensor array 101. One skilled in the art will alsorecognize that the pixel-level MLA is a converging lens, and that aconverging lens may be made in many shapes and complexities, and thatthe mention of particular shapes and/or orientations herein is merelyintended to be exemplary, and is not intended to limit the scope of theinvention. In at least one embodiment, lenses 206 of pixel-level MLA 202are aligned with sensors 106 of photosensor array 101.

Optionally, planarization layer 1101 is added 1202 on top of pixel-levelMLA 202. In at least one embodiment, planarization layer 1101 is formedusing a material with a lower index of refraction than that ofpixel-level MLA 202, creating an optical interface between planarizationlayer 1101 and pixel-level MLA 202. An example of a material that can beused for planarization layer 1101 is silicon dioxide, with an index ofrefraction of approximately 1.5.

In at least one embodiment, optical spacing layer 401 composed ofspacing material is added 1203, for example via deposition or spincoating, on top of planarization layer 1101. Spacing layer 401 may becomposed of any optically transmissive material, and may be applied insuch a manner so that the thickness of layer 401 may be preciselycontrolled to match the optimal focal length of plenoptic MLA 102,adjusted for the index of refraction of spacing layer 401 material. Forexample, in at least one embodiment, optically transmissive photoresistmay be used to apply spacing layer 401. Spacing layer 401 may be appliedusing spin-coating, deposition and/or any other suitable process.Preferably, such a process is optimized so as to ensure the addition ofa very flat and evenly distributed layer.

Material for plenoptic MLA 102 is then added 1204 on top of opticalspacing layer 401. In at least one embodiment, plenoptic MLA 102 isadded 1204 by depositing a layer of photoresist with a preciselycontrolled thickness. This layer of photoresist is developed intoplenoptic MLA 102 using any suitable means, such as for example agrayscale mask and photolithographic process. In at least oneembodiment, the optical properties of plenoptic MLA 102 are determinedin order to provide optimal focus on the plane of pixel-level MLA 202,taking into account all optical materials between plenoptic MLA 102 andpixel-level MLA 202. In at least one embodiment, the layer ofphotoresist has an index of refraction in the range of 1.4-1.6.Plenoptic MLA 102 is shaped 1212, for example by a stamping process. Asdescribed above, in an embodiment wherein the optical material used forplenoptic MLA 202 is a polymer that can be cured using ultravioletlight, the stamp is transparent or semi-transparent to ultravioletlight, allowing the polymer to be cured while the stamp is in place.

In at least one embodiment, spacing layer 401 and plenoptic MLA 102 areconstructed from the same material and are deposited at the same timeusing, for example, a layer of photoresist and grayscale maskphotolithography. The single layer is then shaped to form both spacinglayer 401 and plenoptic MLA 102, according to known photolithographictechniques. In such an embodiment, steps 1203 and 1204 can be combinedinto a single step wherein the material for both spacing layer 401 andplenoptic MLA 102 are deposited; in step 1212, stamping is performed toform both spacing layer 401 and plenoptic MLA 102.

In various embodiments, the various layers described and depictedherein, including pixel-level MLA 202, planarization layer 1101, spacinglayer 401, and/or plenoptic MLA 102, may be manufactured using anymethod or process now known or later developed, including, for example,deposition, spin coating, any lithographic method, ion implantation,silicon doping, and/or diffusion.

Referring now to FIGS. 14A through 14C, there is shown a series ofcross-sectional diagrams depicting an example of fabrication of aplenoptic MLA 102 and spacing layer 401 using a stamping method,according to an embodiment of the present invention. In FIG. 14A, lensmaterial 1402, such as a polymer or other suitable material, has beendispensed on photosensor array 101. For clarity, pixel-level MLA 202 andother aspects have been omitted from FIGS. 14A through 14C. As describedabove, such material 1402 can include, for example, a polymer, siliconnitride, photoresist, and/or any other suitable material. MLA stamp 1401contains indentations 1404 for shaping material 1402 into microlensesfor plenoptic MLA 102. Standoffs 1403 are affixed to photosensor array101 to ensure that stamp 1401 descends to an appropriate distance fromphotosensor array 101 but no closer. These standoffs 1403 may be used toset the height of spacing layer 401. In at least one embodiment,standoffs 1403 are removable, so that they can be detached after theprocess is complete.

In FIG. 14B, MLA stamp 1401 has descended so that it forms material 1402into the appropriate shape for plenoptic MLA 102. In at least oneembodiment, a curing process is now performed, for example by exposingmaterial 1402 to ultraviolet light. In at least one embodiment, MLAstamp 1401 is constructed from a material that is optically transmissivewith respect to the type of light used for curing, so that curing cantake place while stamp 1401 is in the descended position. In at leastone embodiment, standoffs 1403 are constructed to allow any excessmaterial 1402 to escape through the sides.

In FIG. 14C, curing is complete and MLA stamp 1401 has been removed.Material 1402 has now formed into plenoptic MLA 102. If desired,standoffs 1403 can now be removed, along with any excess material 1402.

Although FIGS. 14A through 14C depict fabrication of a plenoptic MLA102, a similar technique can also be used for fabrication of pixel-levelMLA 202 and/or other layers of the optical assembly.

Variations

One skilled in the art will recognize that many variations are possiblewithout departing from the essential characteristics of the presentinvention. The following is an exemplary set of such variations, and isnot intended to be limiting in any way.

No Pixel-Level MLA

In at least one embodiment, pixel-level MLA 202 can be omitted.Photolithographic techniques can be used to deposit material for spacinglayer 401 and plenoptic MLA 102 directly onto the surface of photosensorarray 101. Plenoptic MLA 202 directs light directly onto individualsensors 106 of photosensor array 101.

Multiple Layers of Pixel-Level MLAs

Referring now to FIG. 6, there is shown is a cross-sectional diagramdepicting a detail of an optical assembly 600 including plenoptic MLA102 and a two-layer pixel-level MLA 202, wherein optical assembly 600 isfabricated using a photolithographic process according to an embodimentof the present invention. Here, pixel-level MLA 202 is depicted ashaving two layers 601A, 601B, although any number of layers 601 ofpixel-level MLA 202 can be provided. Such an approach can be usefulwhen, for example, the difference in index of refraction between thematerial used for spacing layer 401 and the material used for thepixel-level MLA 202 is insufficient to obtain the desired degree ofoptical refraction in a single layer. Layers 601 of pixel-level MLAs 202can have the same index of refraction as one another, or differentindexes of refraction.

Pixel-Level MLA Formed Using GRIN

Referring now to FIG. 7, there is shown a cross-sectional diagramdepicting a detail of an optical assembly 700 including plenoptic MLA102 and pixel-level MLA 202C, wherein pixel-level MLA 202C is fabricatedusing a material having a gradient index of refraction (GRIN), accordingto an embodiment of the present invention. Such a material ischaracterized by variations in the index of refraction for differentportions of the material. The use of gradient-index optics allows for agreat degree of customizability in the optical characteristics ofpixel-level MLA 202C. In the example shown in FIG. 7, the opticalmaterial is deposited in such a manner that an area 701 of higher indexof refraction R2 is positioned above each photosensor 106 in photosensorarray 107. These areas 701 of higher index of refraction R2 serve todirect light to photosensors 106, in a similar manner to the microlenses206 described in connection with FIG. 4 and elsewhere herein. Thegradient index may be created using any method now known or laterdeveloped. See, for example, R. S. Moore, U.S. Pat. No. 3,718,383, for“Plastic Optical Element Having Refractive Index Gradient”, issued Feb.27, 1973.

Pixel-Level MLA Modified to Match Optical Properties of Plenoptic MLA

Referring now to FIG. 8, there is shown is a cross-sectional diagramdepicting a detail of an optical assembly 800 including plenoptic MLA102 and pixel-level MLA 202D, wherein pixel-level MLA 202D is fabricatedin a manner that matches certain optical properties of plenoptic MLA102, according to an embodiment of the present invention. Specifically,pixel-level MLA 202D is shaped to form a series of concave areas, orbowls 801. In this example, bowls 801 are highly aligned (in X-Y) withindividual microlenses 116 in plenoptic MLA 102. Such an arrangement maybe useful in situations where plenoptic MLA 102 has significant fieldcurvature. The precise alignment allowed by lithographic techniquesfacilitate shaping of pixel-level MLA 202D to match the field curvatureof plenoptic MLA 102, allowing for better focus and more efficient lightcapture.

Opaque Microstructures on Pixel-Level MLA

FIG. 9 is a cross-sectional diagram depicting a detail of an opticalassembly 900 including plenoptic MLA 102 and pixel-level MLA 202,further including opaque microstructures 901 to block stray light fromneighboring microlenses 116 in plenoptic MLA 102, according to anembodiment of the present invention.

In general, it is optimal if light from one plenoptic microlens 116 doesnot overlap with light from a neighboring plenoptic microlens 116. Inpractice, optical aberrations and diffraction often lead to someoverlap. In at least one embodiment, this problem is addressed by addingoptically opaque microstructures 901 at positions corresponding to theedges of plenoptic microlenses 116; these areas are referred to as lensintersection zones.

Optical assembly 900 can be constructed using any suitable technique.Referring now to FIG. 13, there is shown a flow chart depicting a methodof constructing an optical assembly 900 having opaque microstructures901 as depicted in the example of FIG. 9.

The method begins 1300. Steps 1201 and 1202 are performed substantiallyas described above in connection with FIG. 12, so as to create 1201pixel-level MLA 202 and add 1202 planarization layer 1101. Then, anoptically opaque material is deposited and etched 1301, forming boundarymicrostructures 901. In at least one embodiment, boundarymicrostructures 901 are generated using a binary photomask and dryetching. If needed, multiple iterations may be deposited to reach thedesired height and/or shape. Microstructures 901, which may also bereferred to as baffles, can be constructed to be of any desired height,thickness, and/or shape.

In at least one embodiment, microstructures 901 are upright with respectto photosensor array 107. In other embodiments, microstructures 901 maybe positioned at angles that vary across the surface of photosensorarray 107, for example to match the designated chief ray angle atdifferent positions on photosensor array 107. Thus, differentmicrostructures 901 can have different angles with respect tophotosensor array 107, so that they are all correctly oriented withrespect to the apparent center of the light reaching photosensor array107 from a particular plenoptic microlens 116.

In various embodiments, boundary microstructures 901 can be includedinstead of or in addition to planarization layer 1101 depicted in FIG.11. Accordingly, step 1202, depicted in FIG. 12, can be included oromitted as appropriate.

Steps 1203, 1204, and 1212 are performed substantially as described inconnection with FIG. 12, so as to add 1203 spacing layer, 401, and add1204 and shape 1212 the material for plenoptic MLA 102. As describedabove, any suitable technique, such as grayscale photolithography orsome other method, can be used to create plenoptic MLA 102.

Multi-Layer Plenoptic MLA

Referring now to FIG. 10, there is shown a cross-sectional diagramdepicting a detail of an optical assembly 1000 including a plenoptic MLA102 having multiple layers 1001A, 1001B, according to an embodiment ofthe present invention. In various embodiments, each layer 1001 can havethe same index of refraction or different indexes of refraction. Such aplenoptic MLA 102 can be generated, for example, using successivelithographic steps.

A multi-layer plenoptic MLA 102 as shown in FIG. 10 can be used, forexample, when the index of refraction used for plenoptic MLA 102 isinsufficient to direct the incoming light in the desired direction.Additionally, the use of multiple optical surfaces may improve theoptical performance of plenoptic MLA 202. Any number of layers can beincluded. Accordingly, such a layering technique may be expanded tocreate more advanced plenoptic MLAs.

In the example of FIG. 10, plenoptic MLA 102 is deposited on spacinglayer 401 having a different index of refraction than that of plenopticMLA 102 itself. One skilled in the art will recognize that otherarrangements are possible, including those in which spacing layer 401has the same index of refraction as one or both of the layers 1001 ofplenoptic MLAs 102. Pixel-level MLA 202 and photosensor array 107 areomitted from FIG. 10 for clarity only.

In the above description, for purposes of explanation, numerous specificdetails are set forth in order to provide a thorough understanding ofthe invention. It will be apparent, however, to one skilled in the artthat the invention can be practiced without these specific details. Inother instances, structures and devices are shown in block diagram formin order to avoid obscuring the invention.

Reference in the specification to “one embodiment” or “at least oneembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. The appearances of thephrase “in one embodiment” or “in at least one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

As will be understood by those familiar with the art, the invention maybe embodied in other specific forms without departing from the spirit oressential characteristics thereof. For example, the particulararchitectures depicted above are merely exemplary of one implementationof the present invention.

The functional elements, components, and method steps described aboveare provided as illustrative examples of one technique for implementingthe invention; one skilled in the art will recognize that many otherimplementations are possible without departing from the presentinvention as recited in the claims. The particular materials andproperties of materials described herein are merely exemplary; theinvention can be implemented with other materials having similar ordifferent properties.

The particular capitalization or naming of the modules, protocols,features, attributes, or any other aspect is not mandatory orsignificant, and the mechanisms that implement the invention or itsfeatures may have different names or formats. In addition, the presentinvention may be implemented as a method, process, user interface,computer program product, system, apparatus, or any combination thereof.Accordingly, the disclosure of the present invention is intended to beillustrative, but not limiting, of the scope of the invention, which isset forth in the following claims.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of the abovedescription, will appreciate that other embodiments may be devised whichdo not depart from the scope of the present invention as describedherein. In addition, it should be noted that the language used in thespecification has been principally selected for readability andinstructional purposes, and may not have been selected to delineate orcircumscribe the inventive subject matter. Accordingly, the disclosureof the present invention is intended to be illustrative, but notlimiting, of the scope of the invention, which is set forth in theclaims.

What is claimed is:
 1. An optical assembly, comprising: a photosensorarray, comprising a plurality of photosensors; a spacing layer,comprising a solid optically transmissive material, adjoining thephotosensor array; and a plenoptic microlens array adjoining the spacinglayer, configured to direct incoming light through the spacing layer andtoward the photosensor array, the plenoptic microlens array having a topsurface and a bottom surface; wherein the spacing layer is situatedbetween the photosensor array and the plenoptic microlens array and isconfigured to separate the photosensor array from the plenopticmicrolens array.
 2. The optical assembly of claim 1, wherein theplenoptic microlens array is created using photolithography.
 3. Theoptical assembly of claim 1, wherein the plenoptic microlens array iscreated by stamping and curing.
 4. The optical assembly of claim 1,wherein the spacing layer and the plenoptic microlens array are createdas successive photolithographically deposited layers.
 5. The opticalassembly of claim 1, wherein the spacing layer and the plenopticmicrolens array are created from the same material.
 6. The opticalassembly of claim 1, wherein the spacing layer and the plenopticmicrolens array are created from the same photolithographicallydeposited layer.
 7. The optical assembly of claim 1, wherein theplenoptic microlens array comprises a plurality of plano-convexmicrolenses, each plano-convex microlens comprising: a flat surfaceabutting the spacing layer; and a convex surface.
 8. The opticalassembly of claim 1, wherein the spacing layer and the plenopticmicrolens array are created using photoresist.
 9. The optical assemblyof claim 1, wherein the plenoptic microlens array comprises a pluralityof layers of microlenses.
 10. The optical assembly of claim 1, whereinthe plenoptic microlens array comprises a plurality of microlenses,wherein each microlens corresponds to an integral number of photosensorsof the photosensor array.
 11. The optical assembly of claim 1, whereinthe plenoptic microlens array comprises a plurality of microlenses,wherein each microlens corresponds to a square comprising an integralnumber of photosensors of the photosensor array.
 12. The opticalassembly of claim 1, wherein the spacing layer adjoins the bottomsurface of the plenoptic microlens array.
 13. An optical assembly,comprising: a photosensor array, comprising a plurality of photosensors;a planarization layer adjoining the photosensor array, the planarizationlayer having a top surface and a bottom surface; a spacing layer,comprising a solid optically transmissive material, adjoining the topsurface of the planarization layer; and a plenoptic microlens arrayadjoining the spacing layer, configured to direct incoming light throughthe spacing layer and toward the photosensor array, the plenopticmicrolens array having a top surface and a bottom surface; wherein thespacing layer is situated between the planarization layer and theplenoptic microlens array and is configured to separate theplanarization layer from the plenoptic microlens array.
 14. The opticalassembly of claim 13, wherein: the spacing layer and the plenopticmicrolens array are created from a material having a first index ofrefraction; and the planarization layer is created from a materialhaving a second index of refraction different from the first index ofrefraction.
 15. The optical assembly of claim 13, wherein: the spacinglayer and the plenoptic microlens array are created using photoresist;and the planarization layer is created using silicon dioxide.
 16. Theoptical assembly of claim 13, wherein the spacing layer adjoins thebottom surface of the plenoptic microlens array.
 17. A method formanufacturing an optical assembly, comprising: adding a spacing layer toa photosensor array comprising a plurality of photosensors, the spacinglayer comprising a solid optically transmissive material, adjoining thephotosensor array; and adding a plenoptic microlens array adjoining thespacing layer, configured to direct incoming light through the spacinglayer and toward the photosensor array, the plenoptic microlens arrayhaving a top surface and a bottom surface; wherein the spacing layer isadded in such a manner as to be situated between the photosensor arrayand the plenoptic microlens array and configured to separate thephotosensor array from the plenoptic microlens array.
 18. The method ofclaim 17, wherein the plenoptic microlens array is added usingphotolithography.
 19. The method of claim 17, wherein adding the spacinglayer and adding the plenoptic microlens array comprise addingsuccessive photolithographically deposited layers.
 20. The method ofclaim 17, wherein the spacing layer and the plenoptic microlens arrayare created from the same material.
 21. The method of claim 17, whereinthe spacing layer and the plenoptic microlens array are created from thesame photolithographically deposited layer.
 22. The method of claim 17,wherein adding the plenoptic microlens array comprises adding aplurality of plano-convex microlenses, each plano-convex microlenscomprising: a flat surface abutting the spacing layer; and a convexsurface.
 23. The method of claim 17, wherein adding the spacing layerand the plenoptic microlens array comprise creating the spacing layerand the plenoptic microlens array using photoresist.
 24. The method ofclaim 17, wherein adding the plenoptic microlens array comprises addinga plurality of layers of microlenses.
 25. The method of claim 17,wherein the spacing layer adjoins the bottom surface of the plenopticmicrolens array.
 26. The method of claim 17, wherein adding theplenoptic microlens array comprises adding a plurality of microlenses,wherein each microlens corresponds to an integral number of photosensorsof the photosensor array.
 27. The method of claim 17, wherein adding theplenoptic microlens array comprises adding a plurality of microlenses,wherein each microlens corresponds to a square comprising an integralnumber of photosensors of the photosensor array.
 28. The method of claim17, wherein adding the plenoptic microlens array comprises: stamping theplenoptic microlens array; and curing the plenoptic microlens array. 29.The method of claim 28, wherein: stamping the plenoptic microlens arraycomprises stamping the plenoptic microlens array using alight-transmissive stamp; and curing the plenoptic microlens arraycomprises curing the plenoptic microlens array through thelight-transmissive stamp.
 30. A method for manufacturing an opticalassembly, comprising: adding a planarization layer to a photosensorarray comprising a plurality of photosensors, the planarization layeradjoining the photosensor array, the planarization layer having a topsurface and a bottom surface; adding a spacing layer, comprising a solidoptically transmissive material, adjoining the top surface of theplanarization layer; and adding a plenoptic microlens array adjoiningthe spacing layer, configured to direct incoming light through thespacing layer and toward the photosensor array, the plenoptic microlensarray having a top surface and a bottom surface; wherein the spacinglayer is situated between the planarization layer and the plenopticmicrolens array and is configured to separate the planarization layerfrom the plenoptic microlens array.
 31. The method of claim 30, wherein:adding the spacing layer and the plenoptic microlens array comprisecreating the spacing layer and the plenoptic microlens from a materialhaving a first index of refraction; and adding the planarization layercomprises creating the planarization layer from a material having asecond index of refraction different from the first index of refraction.32. The method of claim 30, wherein: adding the spacing layer and theplenoptic microlens array comprise creating the spacing layer and theplenoptic microlens array using photoresist; and adding theplanarization layer comprises creating the planarization layer usingsilicon dioxide.
 33. The method of claim 30, wherein the spacing layeradjoins the bottom surface of the plenoptic microlens array.
 34. Anoptical assembly, comprising: a photosensor array, comprising aplurality of photosensors; a spacing layer, comprising a solid opticallytransmissive material; and a plenoptic microlens array, configured todirect incoming light through the spacing layer and toward thephotosensor array, the plenoptic microlens array having a top surfaceand a bottom surface; wherein the spacing layer is situated between thephotosensor array and the plenoptic microlens array, and is configuredto separate the photosensor array from the plenoptic microlens arraywith no air gap between the spacing layer, the top surface of thephotosensor array, and the bottom surface of the plenoptic microlensarray.
 35. A method for manufacturing an optical assembly, comprising:adding a spacing layer to a photosensor array comprising a plurality ofphotosensors, the spacing layer comprising a solid opticallytransmissive material; and adding a plenoptic microlens array,configured to direct incoming light through the spacing layer and towardthe photosensor array, the plenoptic microlens array having a topsurface and a bottom surface; wherein the spacing layer is added in sucha manner as to be situated between the photosensor array and theplenoptic microlens array and configured to separate the photosensorarray from the plenoptic microlens array with no air gap between thespacing layer, the photosensor array, and the bottom surface of theplenoptic microlens array.